Transient global amnesia, or TGA, is a brief bout of amnesia, not lasting longer than a day, without causing other problems.

Levitra added transient global amnesia to its label earlier this year. And now, FDA records show that Cialis and Viagra will make similar additions to their labels.

Those label changes don't amount to warnings or precautions. Instead, they'll be listed in the "Post-Marketing" section of the drugs' labels.

There's no proof that any of the erectile dysfunction drugs cause transient global amnesia, which can happen for various reasons; it can even be triggered by sex.

Drug Companies Respond

The drug company Pfizer makes Viagra; Eli Lilly and Company makes Cialis. WebMD asked both companies for their comments on their drug's label change.

Sally Beatty, director of Worldwide Communications for Pfizer, emailed Pfizer's statement, which notes that Pfizer "regularly monitors and evaluates any adverse events reported to Pfizer directly or indirectly through secondary sources. We also routinely conduct reviews of both clinical and post-marketing safety surveillance data. To date, the data do not suggest a causal relationship between the use of Viagra and transient global amnesia."

Pfizer also states that when used as prescribed, Viagra has been shown to be a "safe and effective treatment for erectile dysfunction across a broad range of men with ED," and has been used by more than 35 million worldwide since 1998.

Keri McGrath, a spokeswoman for Lilly, tells WebMD that "we carefully monitor safety data associated with the use of Cialis and we review this data for adverse events on an ongoing basis, and this data is regularly shared with the regulatory bodies globally."